Species diversity, ecology and evolution in a primitive Angiosperm genus:Hibbertia (Dilleniaceae)

Abstract

Among the approximately 130 species ofHibbertia found in Australia, there are tall shrubs, low or trailing shrubs and vines bearing a diversity of leaves as to shape and venation pattern. Flowers are solitary, in leafy cymes or in false spikes, and display various gradual and abrupt transitions from vegetative to reproductive appendages. In the androecium, stamen number is highly variable both between and within species. Some sections have radial symmetry, others bilateral symmetry of the androecium and gynoecium. Follicle number varies from 10 to 1. Basic chromosome numbers of n = 4, 5, 8, 9, 10, 12 and 13 have been found in various sections, and occasional higher numbers, up to n = 64, indicate the presence of polyploidy. Habitats vary from tropical savanna through rain forest margins, wet and dry sclerophyll forests, heaths, sphagnum swamps, and mallee scrub to desert margins. The principal center of diversity is southwestern Australia, less diverse centers are in southeastern and northern Australia. With respect to leaf size, structure and venation; floral symmetry; and chromosome numbers; the diversity found among the species ofHibbertia exceeds that found in all but a few genera of Angiosperms, and is greater than that in any other exclusively woody genus. Nevertheless, individual species are relatively constant with respect to both morphology and ecological preferences.